Removing fluorides from drinking water



Patented Sept. 30, 1941 REMOVING FLUORIDES FROM DRINKING WATER Elias Elvove, Washington, D. 0., asslgnor to the Government of the United States of America, as

represented by the Secretary of the Treasury No Drawing. Application February 12, 1937, Serial No. 125,482

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3'10 0. G. 757) 6 Claims.

The invention described herein, if patented,

' may be used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon.

The present invention relates to a method for removing fluorides from drinking waters. It has been found that the dental hypoplasia, now referred to as chronic dental fluorosis, and also known as mottled enamel" of the human teeth, I

is caused or associated with the presence of toxic quantities of fluoride in the drinking water used by children during the period of teeth development. According to our present knowledge, the teeth become affected when the concentration of fluoride, calculated as fluorine (F) is in excess of about 1 part per million in the drinking water; and within the range of the fluoride concentrations ordinarily met with in drinking waters, the degree of severity of the mottled enamel and the incidence increase with increases in thefluoride concentration.

I. have found that fluorides can be removed from drinking water with the aid of tricalcium phosphate, Caa(PC )4)2, especially when employed I in comparatively large excess in comparison with the quantity of fluoride to be removed, as illustrated below by a specific example.

Since one of the aims is to enable an individual family to treat its own water, I shall describe an adaptation of my method wherein only simple that the water contains about 5 parts per million of fluoride (F), is relatively low in mineral content and has a pH approximately near neutrality, one may proceed as follows:

Into a bottle of about 2 -galloncapacity, place 2 gallons of the water to be treated, add /2 pound of trlcalcium phosphate in finely powdered condition and shake well for about half an hour (or for several shorter periods until the total amounts to about half an hour). Allow to settle and filter through a suitable filter.

It is, of course. to be expected that since natural waters vary greatly in chemical composition, and fluoride-containing waters vary also in their fluoride concentrations, that some of the details of the method, such as the excess of the trlcalcium phosphate to maintain,the time of agitation and mixing, the fineness or state of division of the powder or precipitate, the time to allow for the settling, etc., will have to be adjusted experimentally on the basis of the chemical composition of the water to be treated and its fluoride concentration.

In the specific case mentioned, experience has shown that a 48-hour settling has often been sufflcient to render the upper of the water practically clear even without filtering. Since, however, it is quite simple, even when operating ona comparatively small scale, to utilize a siphonaction for drawing off the water treated, after the solids have settled, and to connect the lower end of the siphon tube with a suitable filter, it is preferable to follow such a procedure and pass the treated water through a suitable filter.

It is apparent that instead of adding the tricalcium phosphate as an extraneously-formed preparation, one can produce this compound directly in the water to be treated by adding aption, since it becomes easier to apply this method even by one who is not versed in the chemical reactions involved and also avoids the possibilities of error in the dosages of the chemicals to be added.

In the specific case mentioned, the charge of 0 A pound of trlcalcium phosphate could be used over again several times for treating additional lots of the water. As may be expected, however,

the number of times a given charge could be used 1. A method for the removal from water of fluorides dissolved in the water, consisting in contacting such fluoride-containing water with the dissolved fluoride content of the water, and

withdrawing the water from such contact.

2. A method for the removal from water of fluorides dissolved in the water, consisting in contacting such fluoride-containing water with preformed tricalcium phosphate in an amount by weight hundreds of times the approximate fluoride content of the water, maintaining such contact for a period of time sufficient to reduce substantially the dissolved fluoride content of the water, and withdrawing the water from such contact.

3. A method for the removal from water of fluorides dissolved in the water, consisting in agitating such fluoride-containing water with even less than that corresponding to the water phosphate for a period of time suflicient to reduce substantially the dissolved fluoride content or the water, and withdrawing the water from such contact.

5. A method for the removal from water of fluorides dissolved in the water in concentrations solubility of calcium fluoride; consisting in con- 'tacting such fluoride containing water with tricalcium phosphate that is substantially free of fluorine, in such large separable excess, comprising by weight hundreds of times the approximate fluoride content of the water, that dissolved fluoride will be taken up by the. insoluble calcium phosphate; maintaining the water in contact with the calcium phosphate for a time sufliciently long to remove a substantial proportion of the dissolved fluoride; separating the water from the solids; and repeating the treatment of fluoridefinely divided tricalcium phosphate in an amount by weight hundreds of times the approximate fluoride content of the water, maintaining the water 'in contact with the calcium phosphate for a period of time sufllcient to reduce substantially the dissolved fluoride content of the water, and withdrawing the water from such contact.

4. A method for the removal from water of fluorides dissolved in the water, consisting in agitating such fluoride-containing water with t containing water with said solids until the fluoride-removing power of the tricalcium phosphate has been substantially exhausted.

6. A method for the removal from drinking water of fluorides dissolved in the water consisting in contacting such fluoride containing drinking water with tricalcium phosphate in an amount of at least 200 parts per one part of fluoride contained in said water, maintaining contactbetween the tricalcium phosphate and the water for a period sufllcient to reduce the fluoride content to a negligible amount, and separating the water from the calcium phosphate and other insoluble solids in the water,

ELIAS ELVOVE. 

